There are many environments where the ability to hear and distinguish a certain noise or sounds from others in the environment is important. For example, in a crowded lecture theater, an audience member listening to a speaker/lecturer may encounter noise from a variety of sources. These could include noise sources inside the theater, such as air conditioning or other ventilation, cellphones of other audience members, people talking or shuffling papers during the speaker/lecturer's presentation, and the like. Noise also could come from outside the lecture theater (e.g. traffic, hallway voices, custodians operating cleaning equipment, and the like). In such environments, a listener's ability to discern or hear desired sounds from others can be diminished. In addition, as a speaker or listener moves about the lecture theater, the sound conditions may change. For example, if the listener is sitting too close to the speaker, or a set of audio speakers, the sound level may be too high. Alternatively, if the listener is too far away from the sound sources, the sound level may be too low. Other noisy environments, such as parties, busy public streets, and stadiums also present hearing challenges.
Noise cancellation systems process noise based on existing pre-determined criteria. For example, some systems, such as those utilizing automatic gain control, utilize a reference level and determine whether a noise signal is above that level. If the noise signal is not above the reference level, then it is considered unwanted noise and is removed. Such systems do not take into account factors which may, for example, make an otherwise low-level signal a desired signal.